The present invention relates to a high pressure fuel supply system using a fuel pump of an internal combustion engine, and more particularly to apparatus for reducing caloric power dissipation of a variable displacement high pressure fuel pump.
Direct injection engines (spark ignition gasoline direct injection internal combustion engines) for vehicles have been developed recently in order to clean exhaust gases and reduce fuel consumption for environmental maintenance. In a gasoline direct injection internal combustion engine, fuel is injected via a fuel injection valve directly into a combustion chamber of a cylinder. The droplet diameter of fuel injected via the fuel injection valve is reduced to promote burning of injected fuel, reduce particular substances in exhaust gas, reduce fuel consumption, and so on.
In order to reduce the droplet size of fuel injected via a fuel injection valve, it is necessary to highly pressurize fuel. Various technologies have been proposed for a high pressure fuel pump for supplying high pressure fuel via a fuel injection valve in a pressurized state (e.g., Patent Documents JP-A-2000-8997 and JP-A-2005-69668).
According to Japanese patent document JP-A-2000-8997, a high pressure fuel flow to supply a fuel injection amount via the fuel injection valve is controlled to reduce the high pressure fuel pump drive power. Electromagnetic valves of two types (a normally opened type and a normally closed type), are used as the flow control mechanism. In both cases, the volume of fuel to be pressurized by the high pressure fuel pump is controlled by adjusting the timing when the suction valve closes during a discharge process.
Japanese patent document JP-A-2005-69668 discloses a high pressure fuel pump equipped with a normally closed type electromagnetic valve as a suction valve. Collision sounds of a valve body during a valve open operation are reduced by supplying a valve open signal at the timing intermediate of a suction process.
In a high fuel pump equipped with a normally closed type electromagnetic valve such as disclosed in Japanese patent documents JP-A-2002-8997 and JP-A-2005-69668, the electromagnetic valve is continuously supplied with electric power, for an extended period in some cases. For example, when fuel is not consumed, such as during engine braking, the high pressure fuel pump does not discharge fuel continuously. In this state, since the electromagnetic valve is maintained in a valve open state, the electromagnetic valve is continuously supplied with an electric power. Therefore, problems arise such as overheating of the electromagnetic valve, an increase in a consumption energy of the whole system, and a large load on the drive circuit. Although there is a method of controlling drive current on a drive circuit side to suppress power consumption by the electromagnetic valve, a current control circuit is generally expensive, so that this current control method cannot be used in an inexpensive system. The present invention has been made in consideration of the above-described issues.